The reflectivity of silver, gold and aluminum granular ultra-thin films deposited on an oxidized aluminum substrate has been measured in a spectral range from 300 to 700 nm. This measurement was done at 45 degrees with p-polarized light, during the deposition of the different metals and also after a 300 degrees C annealing at the end of the evaporation process. Some measurements were also performed in air at different incidence angles with p- and s-polarized light. Plasmon resonance effects of metal particles are seen directly in the reflectivity spectrum.